DESCRIPTION: The proposed research will explore the function of PcaK, a recently described protein from Pseudomonas putida that has the novel ability to function as both a chemoreceptor and a membrane-bound permease. The substrate recognized by PcaK is the aromatic compound 4-hydroxybenzoate. Experiments will explore the transport properties of PcaK and identify structural features and amino acid residues of PcaK that are essential for either chemotaxis or transport, or both. Studies will also be carried out to define methyl-accepting chemotaxis proteins and general chemotaxis proteins in P. putida and to determine which of these or other proteins interacts with PcaK to initiate the transmission of sensory information to the bacterial flagellar motors. PcaK will also be used to test the hypothesis that some permease genes are subject to "regional" molecular control mechanisms that enable bacteria to degrade structurally related aromatic compounds according to a preferred hierarchy. Regulatory elements responsible for repression of 4-hydroxybenzoate transport (pcaK expression) by benzoate, a preferred carbon source, will be identified. The proposed studies should broaden current concepts about mechanisms of bacterial chemoreception and sensory transduction. The results should also lead to the development of a model of aromatic compound detection that extends to diverse bacteria and possibly to diverse members of this large and practically significant group of compounds, many of which are carcinogens.